Furnace heat economizer



April 1941- B. G. caoss 2,236 750 FURNACE HEAT ECONOMIZER Filed April 28, 19 39 3 Sheets-Sheet 1 lnnentor Burl G. Cross M Cittorneg a April 1, B CROSS FURNACE HEAT ECONOMIZER Filed April 28, 1939 3 Sheets-Sheet 2 -Z'mu entor Burl Cross a (Ittorneg a April 1, 1941 Q ss 2,236,750

FURNACE HEAT ECONOMIZER Filed April 28, 1959 3 sheets-Sheet 3 D g\ Zhwentor Burl G. Cross Patented Apr. 1, 1941 UNITED STATES PATENT OFFICE FURNACE HEAT ECONOMIZER Burl G. Cross, Lansing, Mich. Application April 28, 1939, Serial No. 270,486

4 Claims.

This invention relates to heat economizers and particularly economizers of furnace heat.

In furnaces, as now commonly installed, heat extracted from combustion gases is materially less than the permissible maximum, and consequently there is a considerable wasteful delivery of heat to the chimney with discharging smoke and gases.

An object of the invention is to improve a heat economizer having a set of flues extending between inlet and outlet headers for combustion gases and spaced to form passages for a flow of air to be heated by such gases, by providing an additional passage conducting air in intimate proximity to the inlet header and extracting heat from such header.

Another object is to provide a convenient and effective installation for a motor-driven fan supplementing the convection flow of air through said passages and permitting their capacity to be reduced as compared to an installation relying solely on convection flow.

A further object is to install within the outlet header of the described heat economizer a damper variably restricting the outlets of the several flues, and permitting flow of combustion gases to be regulated for either starting or running con- I ditions, so that cooling of such gases below their dew point is avoided.

These and various other objects are attained by the construction hereinafter described and illustrated in the accompanying drawings wherein:

Fig. 1 is a top plan view of the improved economizer, partially broken away to show the arrangement of flues in air passages, as shown by line Il of Fig. 3.

Fig. 2 is a side elevational view of the economizer.

Fig. 3 is a cross sectional view of the outlet header, taken on the line 3-3 of Fig. 2.

Fig. 4 is a cross sectional view on the line 4'--4 of Fig. 2 of a dome within which heated air is collected from the several air passages and particularly showing a baflle for air entering such dome.

Fig. 5 is a fragmentary vertical sectional view, taken on the line 5-5 of Fig. 1, showing the mounting of a motor driving a fan expelling air from said dome.

Fig. 6 is a diametrical sectional view of a thermostatic switch installation.

Fig. 7 is a cross sectional view of said switch, taken on the line 1-1 ofFig. 6.

I In that form of the invention disclosed in Figs. 1..

1-7, the reference characters land 2 designate respectively an inlet and an outlet header for furnace smoke and gases, the inlet header laterally carrying a fitting 3 opening thereinto for connection with the outlet 4 of a furnace 5, and the outlet header carrying an upwardly directed discharge fitting 6 for connection with a smoke pipe (not shown). Connecting said headers is a suitable number of elongated sheet metal flues 1, preferably having a slight upward inclination toward the outlet header and laterally spaced apart to form air passages 8. It is preferred to give said flues a width materially greater than that of the air passages as best appears in Figs. 1 and 3. The walls defining and separating the flues and air passages are parallel and preferably vertical, and provide a large surface area as compared to the capacities of the flues and air passages, thus assuring a considerable heat transfer from the flue gases to air fiowingin said passages. In the aggregate, however, the capacity of the flues sufficiently exceeds that of the furnace outlet to afford the gases a reasonably free flow.

It is, of course, necessary to close the air passages, where they adjoin the headers l and 2, for the exclusion of smoke and gases, and preferably this closure is effected by gradually bringing together the walls of each air passage in close proximity to each header, as is best seen in Fig. 1. In addition to closing the air passages,

this has the effect of forming the gas flues 1 withflaring inlets and outlets, such as considerably facilitate the entry of smoke and gases to i and their exit from the flues.

Seating against the top and bottom faces of the flues and forming upper and lower walls for the 'air passages are sheet metal plates 9 and I0. Discharging into the air passages 8 at their ends adjacent to the header I is an air passage II extracting heat from the header I and formed by a sheet metal plate I 2 suitably spaced from such header and extending around, above and below the latter. The plate l2 and corresponding air passage overlap the passages 8 for a short distance, as best appears in Fig. 2, to assure an adequate flow connection from the passage II to the passages 8. A fitting l3 arranged beneath and at the junctureof the header I and flues 1, projects some distance below the passages 8 and serves to deliver air to said passages and also to the passage l I.

Surmounting the flues 1, in proximity to the outlet header is a sheet metal dome M in communication with the several air passages 8 and serving to collect air from the higher ends of such passages. An air outlet from such dome is formed at its upper medial portion by a cylindrical fitting l5, and within such fitting is installed a fan l6, increasing the velocity of flow through the several air passages. Said fan is driven preferably by a motor I! installed at an opposite side of the dome from the fitting I5, the fan drive shaft extending through the dome, as indicated at iii. In order to minimize sound transmission from the motor to air flowing from the dome, it is preferred to mount the motor on a bracket I9 bolted or otherwise secured to the header 2, a vibration-absorbing pad being interposed between such bracket and header.

The fan IE will have a tendency to draw air primarily from such of the passages 8 as lie directly below the fan, and to check such tendency it is preferred to limit the upflow of air into the mid portion of the dome by a baffle member 2| (see Fig. 4) such member permitting a free upward air flow into the lateral portions of the dome.

To somewhat counteract the tendency of the air to flow directly from the inlet [3 to the dome l4 through the passages 3, it is preferred to provide a baflie in the approximate mid portion of each such passage, serving to deflect the air stream downward. As best appears in Figs. 1 and 2 these battles are formed by indenting the walls of each air passage toward and against each other, as indicated at am, the indentations extending diagonally of said passages to efiect the desired downward deflection of the air stream. The baffles thus formed are spaced from the plates 9 and ID to assure an adequate flow of air above and below such baflies. The described indentations further serve as spacers for the air passage walls, resisting warping thereof and strongly reinforcing the mid portion of the economizer.

Journaled transversely of the header 2 in proximity to its top and to the flue outlets, is a hinge pin 22 fixedly carrying a damper 23 adapted to swing through an approximately sixty degree angle. In one limiting position, such damper lies against the outlet ends of the dues, closing approximately the upper halves thereof. The free edge of said damper has an arcuately reentrant mid portion 24 of a radius approximate- I 1y equaling that of the outlet 6, and assuring a free flow to such outlet when the damper is upwardly swung. Preferably this damper is formed with a plurality of vertical slots 25 in its lateral portions affording a limited flow of gases through such portions, and such slots registering with the vertical walls of the fiues so that said flow must be in close heat-transferring relation to said walls.

Exteriorly of the header 2, an arm 26, fixed on the hinge pin 22., is engaged by a coiled spring 2611, tending to maintain the damper to its open position, shown in Fig. 2. Said arm is further engaged by a link 2! serving to actuate such arm from the core 28 of a solenoid 29 exteriorly mounted on the lower portion of the header 2 by a bracket 30. Controlling the circuit 3| of such solenoid and of the fan It is a mercury tube switch 32, installed within a casing 33 exteriorly mounted on the dome l4. Said switch is secured on a rock-shaft 34 suitably journaled within the casing 33 and acted on by a spiral bimetallic spring 35.

In operation of the described economizer, the fiow of hot gases through the header I and lines 1 induces through the passages 8 and II, a con- Vectional air flow, which is further increased by the fan IS. The transfer of heat to such passages materially reduces the temperature of the gases, as delivered to the header 2, but avoids a temperature reduction of the gases below their dew point, or such as would unduly detract from chimney draft.

When the flues are cold or approximately so, as on starting combustion in the furnace or building up combustion from a low point, the

damper 23 is held in its fully open position by the spring 26a, so that the gases may flow in a maximum volume to bring the fines up to their operating temperature. When the temperature acting on the thermostatic spring 35 rises to a predetermined value, the switch 32 is shifted to its circuit-closing position, thus energizing the solenoid 29 and the fan motor. The solenoid thereupon downwardly retracts the core 28. shifting the damper to its closed position and maintaining such position during normal operation of the furnace, sufiiciently retarding the gases to assure a predetermined transfer of heat therefrom to the air. Upon a reduction of furnace combustion such as to result in opening of the thermostatic switch 32, the fan motor and solenoid are deenergized and the spring 26a again opens the damper.

Avoidance of baflies acting on the discharging gases is believed an important factor in efficiency of the described economizer, since baille installations entail materially increased resistance to flow, whereas the described construction affords the gases an even freer flow than would the smoke pipe section, which the economizer replaces. Any leakage of smoke or gases is avoided by employing joints sealed either by lap bends or by welding.

While the described installation effects economy by usefully heating air, it is to be noted that the invention, in its broader aspects, em-

' braces possible modifications for water heating purposes.

The invention is presented as including all such modifications and changes as come within the scope of the following claims.

What I claim is:

l. A heat economizer comprising an inlet header and an outlet header for furnace gases. spaced apart in an approximately horizontal direction, a plurality of fines connecting said headers and laterally spaced to form passages for the flow of air to be heated by the gases, and a damper hinged within the outlet header adjacent to the tops of the fiues, and extending downwardly in one position across the outlets of all of the fiues to obstruct the upper portions of the outlets, and means exterior to the outlet header for angularly adjusting said damper to vary its obstructing effect.

2. A heat economizer as set forth in claim 1, said damper being formed with a plurality of openings located substantially in the plane of said air passages and affording a flow of gases in close proximity to the air passages, when the damper is in said downwardly extending position.

3. A heat economizer comprising an inlet header and an outlet header for furnace gases, a plurality of flues elongated in an approximately horizontal direction between said headers and adapted to deliver gases from the inlet header to the outlet header, and spaced apart to form passages for the flow of air to be heated by said gases, said flues and passages having a vertical extent largely exceeding their individual width, top and bottom closures for said air passages, afiording a bottom air inlet to such passages adjacent to the inlet header and a top air outlet in proximity to the outlet header, and means forming a passage of a capacity materially less than the aggregate capacity of the first mentioned passages, having an air inlet substantially 

